Chromatography is the separation of a mixture of compounds (solutes) into separate components. This separation permits the composition of all or part of the mixture to be determined. In gas chromatography, a gas chromatograph (commonly called a “GC”) is utilized to separate and determine the quantities of components of a gas mixture. A gas chromatograph performs these functions by taking a sample of the gas mixture to be analyzed and injecting it into a carrier gas stream, such as helium or hydrogen, which then carries the gas sample through one or more tubes (referred to as columns) that are packed with a very fine particulate material. Each of the particles of this material are coated with a film from liquid that controls the rate at which the different components of the gas sample are absorbed and de-absorbed by the particulate material. This rate of absorption and de-absorption also varies relative to each of the different components. Because of this differing rate of absorption and de-absorption, certain gas molecules related to one type or component of gas will exit the column more quickly than some of the other components will. This process of separation of components permits a detector located at the end of the column to quantify the amount of a particular component that is present in the mixture.
Due to their complexity, conventional field-mountable gas chromatographs tend to be large devices. In order to reduce the overall size of a gas chromatograph, efforts have been made to reduce the size of the different components that make up a gas chromatograph. One such component is the sample valve that controls the supply of a gas sample to a column. A number of compact sample valves have been developed, including those disclosed in U.S. Pat. No. 4,869,282 to Sittler et al.; U.S. Pat. No. 6,374,860 to Xu et al.; U.S. Pat. No. 6,453,725 to Dahlgren et al.; U.S. Pat. No. 6,742,544 to Bergh et al.; and U.S. Pat. No. 6,896,238 to Wang. While these conventional valves are compact and provide a number of benefits, they are highly complex and/or not adapted for use in a highly compact and modular field mountable gas chromatograph.
Based on the foregoing, there is a need in the art for a compact sample valve of simple construction, which is adapted for use in a highly compact and modular field mountable gas chromatograph. The present invention is directed to such a sample valve.